1. Field of the Invention
The present invention relates to a structure of an orifice plate for an engine mount filled with a magnetorheological (“MR”) fluid, and more particularly, to a structure of an orifice plate in which magnetic field is formed in a perpendicular direction in an entire channel in which the magnetorheological fluid flows so as to efficiently control a flow of the magnetorheological fluid filled in the engine mount.
2. Description of Related Art
An engine is installed in an engine room of a vehicle body through an engine mount to attenuate vibration generated from the engine. As the engine mount, a rubber mount using inertia force of a material and a hydro-mount filled with liquid therein and attenuating vibration as an inertia effect of the liquid are primarily widely used.
Between them, the hydro engine mount is configured to attenuate vibrations in a high frequency domain and a low frequency domain to be widely used in various vehicle types.
In the hydro engine mount, a hydro liquid is received in an internal space where an insulator and a diaphragm are formed, however, an orifice plate is mounted on the internal space, which is partitioned into an upper fluid chamber and a lower fluid chamber.
The orifice plate has an annular channel in which the hydro liquid flows to the inside along on a border thereof and may additionally have a decoupler mounted on the center thereof. In addition, a stud coupled with the insulator is coupled with a bracket of the engine. Therefore, when the insulator made of an inertia material is repetitively inertially compressed and restored depending on a weight applied to the stud, the hydro liquid flows to the upper fluid chamber and the lower fluid chamber through the channel. The flow of the hydro liquid vibrates the decoupler, however, the vibration of the high frequency domain is attenuated by the vibration of the decoupler and the vibration of the low frequency domain is attenuated by the flow of the hydro liquid through the channel.
Meanwhile, the hydromount may be filled with an MR fluid instead of the general hydro liquid. The magnetorheological fluid as suspension in which smooth particles having magnetism are mixed with a synthetic hydrocarbon liquid has shear stress that varies depending on the intensity of a magnetic field formed therearound.
Accordingly, the hydromount filled with the MR fluid is configured to control dynamic stiffness and an attenuation characteristic of the mount according to an operation condition of a vehicle by additionally installing a coil to the orifice plate and controlling application of current to the coil so as to form the magnetic field around the channel through which the MR fluid passes.
Meanwhile, a control method of the MR fluid in the related art is shown in FIG. 1B. The orifice plate in the related art has a structure in which a channel opened vertically is installed so that the MR fluid flows to the upper fluid chamber and the lower fluid chamber, however, the coil is mounted to be positioned at one side of the channel and the flow of the MR fluid is controlled by applying the current to the coil.
The MR fluid has a flowing characteristic similar as a general hydro liquid when the magnetic field is not formed therearound, however, when the magnetic field is formed therearound, particles form a line, such that the MR fluid has a changed flowing characteristic. That is, when the magnetic field is not formed, the shear stress of the MR fluid is calculated by a value acquired by multiplying viscosity and a shear rate by each other, however, when the magnetic field is formed, the shear stress of the MR fluid is calculated by adding breakdown shear stress to the multiplying value the viscosity and the shear rate. The breakdown shear stress increases in proportion to the intensity of the applied magnetic field.
However, as shown in FIG. 1B, a flow direction of the MR fluid and a forming direction of the magnetic field should be perpendicular to each other in order to arrange the particles in the MR fluid to be perpendicular to the flow direction.
In the know method, the coil is arranged at one side of the channel at a predetermined interval, and in section “A” and section “C”, the magnetic field is perpendicular to the flow direction of the MR fluid, but in section “B”, the magnetic field is formed in a direction parallel to (the flow direction of the MR fluid), thereby deteriorating control efficiency. That is, in section “A” and section “C”, the magnetic field passes through the MR fluid while being perpendicular to the flow direction of the MR fluid, but in section “B”, the magnetic field is formed in a direction parallel to the flow direction of the MR fluid and does not thus pass through the MR fluid, and as a result, the control efficiency deteriorates.
Therefore, the deteriorated control efficiency is restored by increasing a current value applied to the coil or further lengthening the channel, but the restored control efficiency causes the volume to be increased and a caloric value to be increased.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.